The present invention is related to the field of master/slave control systems that enable a user to manipulate objects and that provide haptic or tactile feedback to the user, and more particularly to master/slave systems used for surgical procedures There is a trend toward increasing use of "minimally-invasive" surgical techniques, meaning techniques in which medical tools are inserted into a patient's body through a relatively small opening in the skin and manipulated from outside the body. In one example of a minimally invasive surgical technique known as "balloon angioplasty", concentric catheters are inserted into a patient's body and guided into a restricted blood vessel, such as a cardiac artery or a peripheral blood vessel suffering a blockage. One of the catheters, called a "balloon catheter" because it has a balloon-like inflatable chamber near the end, is guided into the blood vessel. The balloon-like chamber is inflated to stretch the vessel in the region of the blockage, so that the restricted passage is enlarged.
It is known to use master/slave control systems for some types of minimally-invasive medical procedures. Master/slave control systems are generally configured with a control that can be manipulated by a user, an actuator that holds a tool used in the procedure, and an electromechanical interface between the control and the tool. The electromechanical interface causes the tool to move in a manner dictated by the user's manipulation of the control. An example of a medical use of master/slave systems is in conjunction with an exploratory procedure known as "laparoscopy". During laparoscopy, a physician manipulates a control on a master device in order to maneuver an elongated camera-like device known as a "laparoscope" within the abdominal cavity. The movement of the laparoscope is actually effected by a slave device in response to signals from the master device that reflect the movement of the control by the physician. During the procedure, the physician receives visual feedback directly from the laparoscope. In addition to serving the diagnostic purpose of enabling the physician to examine the abdominal cavity, the visual feedback also enables the physician to properly maneuver the laparoscope.
Master/slave systems provide benefits that the direct manipulation of a surgical tool by a physician does not. Sometimes it is beneficial for the physician and patient to be physically isolated from each other, for example to reduce the risk of infection. A master/slave system may provide greater dexterity in the manipulation of small tools. Also, a master/slave system can be programmed to provide effects not achievable by a human hand. One example is force or position scaling, in which subtle movements on one end either cause or result from larger movements on the other end. Scaling is used to adjust the sensitivity of tool movement to movement of the control. Another example is filtering, such as filtering to diminish the effects of hand tremor or to prevent inadvertent large movements that might damage tissue.
In contrast to procedures such as laparoscopy in which the medical tool provides visual feedback, other minimally invasive procedures rely on other forms of feedback to enable a physician to maneuver a medical tool. For example, imaging apparatus is used in conjunction with balloon angioplasty to enable the physician to track the location of the end of the catheter or wire as it is threaded into an artery. This is also the case in interventional radiology. During these procedures the physician also receives tactile or haptic feedback via the tool itself, i.e. a catheter or wire. For example, the physician can feel frictional resistance if the catheter is being moved along the wall of an artery. Haptic feedback is an important component of the sensory information used by the physician to successfully carry out these types of procedures.
Master/slave systems have not been used in conjunction with procedures such as vascular catheterization or interventional radiology. Procedures such as these require very fine control over the movement of the tool within the patient, and also fine sensing of the subtle haptic feedback received via the tool. Heretofore these requirements have been met by the human hand interacting directly with the tool. However, it would be desirable to use master-slave control systems in such procedures, so that features such as force or position scaling and tremor reduction as discussed above can be taken advantage of.